The purpose of this study is to examine the impact of television on adolescent sleep/wake patterns in the context of a controlled experiment with Vietnamese villages lacking both television and electricity. Accumulating evidence indicates that increasing numbers of adolescents are going to bed later and getting by on less than optimal sleep in most areas of the globalizing world. The convergence of maturational processes with media access and related social changes appear to play a role in these trends. The research plan builds on a unique opportunity to identify social-ecological factors that contribute to the development of adolescent sleep and circadian changes within a randomized experimental design. Introducing television will combine biological and social stimuli via access to lighted screens and engaging stimuli, with altered social interactions around television watching. We will examine sleep patterns and associated neurobehavioral and health statuses in all adolescents aged 12-18 (n=107) residing in a matched pair of experimental television-receiving and control villages. Actigraphy in adolescents will be combined with measures of pubertal status, behavioral alertness, sleep quality, school attendance and performance, and mental and physical health. The study design puts adolescent sleep behavior in social context at 3 levels of analysis, family (household), community (village), and culture (Vietnamese Tai). Household measures include adolescent and parent sleep habits, daily routines, perceived well-being, and GPS tracking to gauge time at key sites (television, home, school, fields), time together, and ranging distance. Village-wide data on each community member are collected in the main project, which this study will join. Measures relevant to our hypotheses include amount of television viewing, GPS-mapped social geography, demographics, and perceived stress, life satisfaction and social status. Ongoing ethnography probes sleep attitudes, practices, and meanings. This research will provide the first direct test for causal links between television and changes in adolescent sleep. We test whether television-watching youth show changed sleep timing, amount, and quality; whether puberty, gender, and parental monitoring influence these effects; and whether school performance and health indices suffer. Findings will directly address questions about whether and how developmental processes (puberty) interact with social ecology (community-level television introduction and household-level conditions) to produce adolescent vulnerability to sleep restriction and disruption, and with what functional and health consequences. Previous research on these questions has been hampered by inability to establish causal influences: we capitalize on a randomized experiment to overcome that difficulty.